* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
.back{
    position: absolute;
    top: 20px;
    right: 10px;
    font-size: 30px;
    text-decoration: none;
            color: black;
}
body>img {
    height: 100%;
    width: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: -1;
}

.logo {
    position: absolute;
    top: 20px;
    left: 40px;
    display: flex;
}

.logo img {
    height: 40px;
}

.logo div {
    font-size: 28px;
    align-self: end;
}

/* 内容居中 底色 */
body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
}

/* 整体登陆盒子 */
.box {
    position: relative;
    width: 380px;
    height: 450px;
    background: white;
    border-radius: 8px;
    overflow: hidden;
}
/* 表单背景 */
form>img {
    opacity:2;
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
}

/* 登录form表单 */
.box form {
    position: absolute;
    inset: 4px;
    padding: 50px 40px;
    border-radius: 8px;
    z-index: 2;
    display: flex;
    flex-direction: column;
}

/* 标题 */
.box form h2 {
    color: #23242a;
    font-weight: 500;
    text-align: center;
    letter-spacing: 0.1em;
    font-weight: 700;
}

/* 输入框盒子 */
.box form .inputBox {
    position: relative;
    width: 300px;
    margin-top: 35px;
}

/* 输入框 */
.box form .inputBox input {
    position: relative;
    width: 100%;
    padding: 20px 10px 10px;
    background: transparent;
    outline: none;
    border: none;
    box-shadow: none;
    color: #23242a;
    font-size: 1em;
    letter-spacing: 0.05em;
    transition: 0.5s;
    z-index: 10;
}

/* username和passward文字样式 */
.box form .inputBox span {
    position: absolute;
    left: 0;
    padding: 20px 0px 10px;
    pointer-events: none;
    color: #676767;
    font-size: 1em;
    letter-spacing: 0.05em;
    transition: 0.5s;
}

/* 有效输入和获取焦点时 span上移 文字减小 */
.box form .inputBox input:valid~span,
.box form .inputBox input:focus~span {
    color: #23242a;
    font-size: 0.75em;
    transform: translateY(-34px);
}

/* 白色横线 */
.box form .inputBox i {
    position: absolute;
    left: 0;
    bottom: 0;
    width: 100%;
    height: 2px;
    background: #fff;
    border-radius: 4px;
    overflow: hidden;
    transition: 0.5s;
    pointer-events: none;
}

/* 有效输入和获取焦点时  横线变高 */
.box form .inputBox input:valid~i,
.box form .inputBox input:focus~i {
    height: 44px;
}

/* 忘记密码和注册盒子 */
.box form .links {
    display: flex;
    justify-content: space-between;
}

/* a链接 */
.box form .links a {
    margin: 10px 0;
    font-size: 0.75em;
    color: #676767;
    text-decoration: none;
}

.box form .links a:hover {
    color: #309cff;
}

/* 登录按钮样式 */
button {
    border: none;
    outline: none;
    padding: 9px 25px;
    background: #309cff;
    cursor: pointer;
    font-size: 0.9em;
    border-radius: 4px;
    font-weight: 600;
    margin-top: 10px;
}

button a {
    text-decoration: none;
    color: #fff;
}

button:active {
    opacity: 0.8;
}

.imgs {
    margin-top: 20px;
    display: flex;
    justify-content: space-between;
}

.imgs img {
    width: 30px;
    height: 30px;
}
.butt{
    position: fixed;
    bottom: 20px;
    text-align: center;
    opacity: 0.5;
}
.gou{
    margin-top: 10px;
    display: flex;
    align-self: center;
    letter-spacing: 1px;
    justify-content: space-between;
}
.gou span{
    color: #309cff;
    text-decoration: solid;
    cursor: pointer;
}